Devices for the therapeutic administration of asthma medication play a large and important part in the control of the disease. In addition to the preventative effects of regular prescribed dosing, with the onset of an asthma attack, it is of vital importance that therapeutic medication be administered promptly and in a proper amount. The most effective way to deliver asthma medication is by inhalation, and by far the most popular means for delivering the medication for inhalation is the metered dose inhaler (MDI) which allows the dispensation of a controlled amount of medication in an aerosol form.
The standard form for an MDI dispenser is a metal canister including an integral dose dispensation nozzle. The medication is under pressure within the canister, and each activation of the valve mechanism releases a measured or metered amount of the medication. Typically, a canister contains sufficient medication for approximately 200 doses.
A major deficiency of the MDI is the lack of a visual dose counter to advise the patient as to the amount of medication remaining in the canister. Accordingly, the patient must be extremely cautious in determining when a canister should be discarded and a new canister used. While patients can become somewhat adept in determining the approximate amount of medication remaining by hefting the canister, or by placing it in water and observing the degree of buoyancy, such procedures provide only general indications of the fill status of the canister. Other, similar attempts to determine the likely useful life of a canister, such as by dividing the number of daily doses prescribed into the number of needed actuations specified by the manufacturer of the canister, can similarly only serve as a guideline. Further complicating the ultimate decision is that, although medication may remain in the canister, proper dosing cannot be assured after a specified number of actuations. Thus, while the canister may appear to remain viable for use, due to the existence of medication therein, there still remains a risk that an incorrect amount of medication will be dispensed if the medication level is too low.
It is accordingly a purpose of the present invention to provide an apparatus which allows the amount of medication in an MDI canister to be determined with practical accuracy.
A further purpose of the present invention is to provide an apparatus for determining the amount of medication in an MDI canister which is convenient and portable.
Yet another purpose of the present invention is to provide an apparatus of the aforementioned type which is accurate, easy to read, and efficient in operation.